The present application relates generally to multi-stage turbines and more particularly relates to interstage seals within multi-stage turbines.
In general, turbine engines combust a mixture of compressed air and fuel to produce hot combustion gases. The combustion gases may flow through one or more turbine stages to generate power for a load and/or compressor. A pressure drop may occur between stages, which may allow leakage flow of a fluid, such as combustion gases, through unintended paths. It is desirable to confine the combustion gases within a defined annular flow path to shield certain rotor parts and to maximize power extraction. Moreover, turbine rotor wheels which support the buckets (blades) are subjected to significant thermal loads during their operating life and thus need to be cooled. Therefore, seals, for example, mechanical seals may be disposed between the stages to reduce fluid leakage between the stages and also prevent the turbine rotor wheels from direct exposure to hot gases. Unfortunately, the seals may not be field maintainable, or a substantial amount of work may be required to replace the seals in the field. In addition, the shape of the seals may make access to internal components of the turbine more difficult. Furthermore, the seals may require additional components, such as spacer wheels between two turbine rotor wheels to ensure proper axial and radial alignment of the seals. Static seals may also be used that require axial extensions from the two turbine rotor wheels which meet in the middle to accommodate the static seal. However, this does not isolate turbine rotor wheels from the hot gas path, thereby necessitating higher performance alloys for rotor parts at high cost for withstanding the harsh temperatures in the event of hot gas ingestion. In addition, the static seals cannot be applied to flange bolted rotor architectures, where access to wheel flange bolts is required during assembly/disassembly.
There is therefore a desire for improved interstage sealing systems for multi-stage turbines. Such sealing assemblies should improve overall system efficiency while being inexpensive to assemble, fabricate and providing an increased life for the associated parts.